BGA package design and common defects
Author:Lu Chunhua Time:2021-06-09 16:48 Browse(824)
BGA package design and common defects, touch screen and OLED Forum
Correct design of BGA package - W, ~ + T / i1l    x! S! S7 ~2 {9 dBall grid array packaging (BGA) is becoming a standard packaging form.
it has been seen that BGA with 0.05 to 0.06 inch spacing can achieve remarkable results.

BGA package design and common defects

the next step of packaging development is likely to be chip level packaging (CSP).
this kind of packaging is smaller and easier to process.
/ \; a* K2 l& U. q$ \1 U5 K0 y) u2 x# T; Q1 X- I4 HBGA design rules2 S2 y   [ 7 Q( f! v$ H6 @% i7 ~* C6 o    e# ~2 q( gBump collapse technology, that is, solder joints formed by solder ball end sinking to the substrate during reflow soldering, can be traced back to the mid-1970s.
however, it has not developed rapidly until now.
at present.
Motorola, IBM, citizen, ASAT, LSI Logic, Hestia and Amkor provide BGA products in addition to using this package in their own products.
# B "I: O # Y / T # A / D) e1 X4 Y0 N8 |; U5 I' xAnother major advantage of BGA is its high yield.
users such as Motorola and Compaq claim that there are no defects in their 0.05 inch pitch packages with 160 to 225 I / O leads.
in other fully automated factories.
the failure rate of fine pitch devices with the same number of I / O leads is 500 or 1000 ppm.
in other fully automated factories, there is no defect in the 0.05 inch pitch packages with 160 to 225 I / O leadsAt present, BGA packages with 400 to 700 I / O leads are being further developed.
Japan even reported the research and development results of BGA packages with 1000 I / O leads.
at present.
the standard has not been fully formulated. JEDEC document only specifies the basic spacing of 1 mm, 1.27 mm and 1.5 mm.
the size range of the substrate is 7 to 50 mm.
the coplanarity is less than 200 μ m.
3 F    z$ }* W/ q" g3 Q9 j# j( Z: m5 A$ `9 D1 l9 ? Limitations of BGA: S5 R' K9 \4 P0 p( n8 A    d/ J' s; P    c) t( {8 n# MMany users complain about the poor visibility of BGA Solder Joints.
BGA Solder Joints can not be detected by naked eyes.
in fact.
due to the increasing number of lead wires of parts, this situation will occur in any modern electronic assembly process.
with low-cost x-ray device and good design rules, relatively simple detection can be carried out.
& B / Q & ^ 9}% v.
I / C6 {4G   ?..& @. k' N6 U; `% V9 T6 R5 I "A4 g the current wiring design (footprint) includes printed wire combination, through hole and 0.02 inch round surface pad.
the size of the solder ball on the device will inevitably affect the pad size.
some engineers pasted solder mask on the pad surface to reduce the device movement and solder paste flow during reflow soldering.
this method was adopted.
in this paper, the design of V9 T6 R5 I" A4 G is introducedThe solder joint is easy to crack during heating, so it is not advisable.
the solder joint is easy to crack during heating3 F0 }- U+ Q% ?' a( o) s# s6 i( F. m9 r.
K. m3 ?/ If the gap between the copper pad and the solder mask coating is standard, the standard solder mask design rules should be adopted.
this simple layout allows wiring on both surfaces of the printed circuit board.
even the devices with 1 or 1.27mm spacing and more I / O numbers will have wiring problems between the solder balls.
select the devices with smaller spacing but "blank" in the center, This problem can be overcome.
there may be only four rows of solder balls on the outer edge of BGA in the center blank.
the routing problem is reduced.
! D    L) p5 Q- K& Z$ r3 o9 N2 R) \ \ + V) V $B3 o (m) through hole mounting! g0 L3 p; W+ A1 B8 u; \' r6 ?& W! R5 T( \( `Some companies use traditional vias as mounting pads for ceramic BGA and more commonly used plastic devices.
at this time.
vias become mounting pads and interconnects through printed boards.
this is ideal for reflow soldering design.
but not for wave soldering products.
remember that wave soldering will cause secondary reflow of BGA on the top of printed boards.
: F (g3t0f5v (K.
t) is the best choice for reflow soldering design_ 7 ["G. O3 V ([, I & F] when using the through-hole mounting method, it is necessary to ensure that the volume of the through-hole matches the printing amount of the solder paste.
when using the through-hole mounting method, it is necessary to ensure that the volume of the through-hole matches the printing amount of the solder pasteWith this technology.
the solder paste will fill the through hole, If this important factor is not taken into account,
the solder ball will sink into the solder joint.
for ceramic BGA,
the high temperature solder ball can only be located on the surface of the through hole.
when the size of the through hole decreases,
the problem is not so serious.
however, when the internal wiring is carried out.
it does affect the wiring of the complex multilayer printed circuit board.
in this paper, the design of the high temperature solder ball is introduced   F; y/ k' f6 @9 N; g& x- b" ? 9} 3 F "L1 | (J5 R6 s) the underfill of the printed circuit board can be tested by the top of the through hole connected to the selected test pad.
in some cases.
the parts manufacturer sets the test point on the top of the BGA package substrate, In order to directly detect the package surface.
if through hole mounting is used in assembly operation.
the test can be carried out by directly detecting the through hole.
! i" X# v- C# F; A+ E% X/ U' N; } 1 R/ J" v" G    zBeware of warpage during reflow soldering.
larger plastic packages may cause warpage.
in some cases.
warpage can be seen in the cladding and substrate, This will cause the contact between the external connection point and the pad to be minimized.
some engineers point out that warpage will occur in die and glass epoxy substrate.
this problem can be overcome to some extent by improving the layout of spherical end points of spare parts.
and limiting the size of the used dieIf solder paste is used instead of flux reflow process, the possibility of this kind of special failure will be reduced, because solder paste has lower coplanarity requirements.
for traditional glass / epoxy substrate.
leadless plastic BGA is used, There will be no welding failure.
because the parts matrix is also made of similar epoxy resin.
and the coefficient of thermal expansion is matched with most applications.
in some special applications.
cracks will appear in the solder joint at the corner of the device, This may be due to the stress generated here.
for plastic BGA devices,
popcorn like cracks may appear.
because during reflow soldering, moisture will expand inside the parts.
at this time,
cracks will appear at the edge of the device between the substrate and the cladding.
if this phenomenon occurs during repair,
the device will be heard to emit "split, split, split" noise The popping sound is called popcorn.
appropriate moisture-proof package must be selected to reduce the possibility of popping.
learn more about PCB related departments, and log on the official website of jiepei X: C6 N0 W$ n( P- [. l0 ]    x$ \) k' D' r    J) K4 q: U+ Z.
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